This invention relates to an improved method for purifying TiO.sub.2 ore which contains numerous impurities. The purified ore can be used to make TiO.sub.2 pigment or titanium metal or be used in any other process where a purified TiO.sub.2 ore is required.
Currently, approximately 75 percent of the titanium minerals produced in the world are utilized by the pigments industry to produce TiO.sub.2. In the production of TiO.sub.2 by the chloride process, beneficiated ore is used which generally contains about 55-96% TiO.sub.2. However, known beneficiation processes do not appear to be capable of satisfactorily purifying TiO.sub.2 ore which contains numerous impurities such as alkali metals, alkaline earth metals, rare earth metals, iron, aluminum, phosphorus, thorium, uranium, chromium, manganese, silicon, vanadium, and yttrium. These impurities may be present as oxides, salts, or other complex forms and generally cannot be readily removed by conventional mechanical means or even conventional chemical means. Especially detrimental to the chloride process are such ores which contain in considerable quantity the impurities of iron, calcium, silicon, aluminum, phosphorus, magnesium, barium and strontium, and radionuclides such as thorium and uranium. For example, phosphorus can cause processing problems in the TiO.sub.2 process, and thorium and uranium may concentrate in the TiO.sub.2 process and present a potential health hazard. Also, the impurities of aluminum, phosphorus, silicon, thorium, and uranium are additionally a problem because they are especially resistant to removal by conventional mechanical or chemical means.
Being able to remove such impurities efficiently would be highly desirable because known sources of TiO.sub.2 ore not containing such impurities are becoming increasingly scarce and expensive. Conversely, there exist large bodies of inexpensive carbonatite anatase ores which are rich in TiO.sub.2 but also contain significant quantities of such impurities. Moreover, while other processes to purify TiO.sub.2 ore are known, it appears that they either require additional, more complex or more expensive processing steps or are deficient in one or more benefits as compared to the process of this invention.
The following information is disclosed which may be of interest to this invention:
U.S. Pat. No. 4,176,159 discloses a process for the removal of impurities from titanium minerals. The process requires high temperature calcining, cooling, reducing, cooling, magnetic separation, mineral acid leaching, neutralizing, and washing.
U.S. Pat. No. 4,038,363 discloses upgrading of titanium values in a slag such as Sorels slag by roasting with an alkali salt, leaching with sulfuric acid in two stages, and calcining.
Japanese patent 48,102,712 discloses dephosphorization of titanium concentrates using caustic alkali after prior removal of iron.
Japanese patent 87-33058/47 discloses production of rutile-type titanium dioxide sol by heat treating hydrated titanium oxide and alkali metal hydroxide and maturing in hydrochloric acid aqueous solution.